The present invention relates to a part painting apparatus for applying a painting treatment to a part (generally a plastic molded component) of a device such as a lamp fixture for a vehicle, including a lens, lamp body, or decorative frame, as well as desired portions of other parts. More particularly, the invention relates to a part painting method and painting apparatus using a paint gun.
As shown in FIG. 6, in a known method and apparatus for applying an antifogging paint to the inside of a lens, which is a synthetic resin molded component, the lens 1 is mounted on a jig 2. A paint mask composed of a parent mask 3a and child mask 3b is placed on top of the lens 1 such that only the surface to be painted 1a of the lens is exposed. Painting is conducted with a paint gun 5 from above the surface to be painted 1a of the lens.
With the aforementioned conventional method and apparatus, however, because the surface to be painted 1a is facing upward, it is easy for dust in the air and paint residue that peels and falls from the paint gun to adhere to the surface 1a. 
In addition, paint adhered to the child mask 3b from the spray paint may build up thickly, as denoted at reference numeral 7, at the inner peripheral edge of the mask 3 (child mask 3b) which defines the surface to be painted 1a, and excess paint, as denoted by reference numeral 8, may drip down on the surface to be painted 1a, or paint residue that has peeled off of the child mask 3b may drop off, creating a surface that is not proper for painting.
In order to prevent damage by drops of excess paint and paint residue, it is preferable to change the mask 3 (child mask 3b) often so that paint does not build up thickly at the inner peripheral edge of the mask 3 (child mask 3b). It is also necessary to clean the mask after it has been removed from service. Such actions are quite bothersome in practice.
Further, a jig 2 is necessary to support the lens 1, which makes the structure of the apparatus more complicated.
In view of the problems with the aforementioned conventional method and apparatus, an object of the present invention is to provide a part painting method and apparatus in which the foregoing problems, such as dust accumulation, dropping of paint residue and dripping of excess paint, have been eliminated by applying spray paint to a surface to be painted which is slanted downward with respect to vertical.
To achieve the foregoing objects, a part painting method according the invention includes the steps of covering a portion of a part with a mask body and painting a surface of the part that is exposed through the mask body with a paint gun in such a manner that the part is positioned and fixed on the rear side of the mask body of which the front side, which functions as a mask with respect to the spray paint from the paint gun, is arranged slanted downward with respect vertical. Painting is performed with the mask body slanted at a predetermined angle so that excess paint that may drip from the mask body will not drip onto the part. Even if excess paint drips from the mask body, it will not drip onto the part to be painted.
The part painting apparatus is provided with fixing means for positioning and fixing the part. The mask body is slanted at a predetermined angle with the front side thereof, which functions as a mask with respect to the spray paint from the paint gun, slanted downward so that excess paint adhered to the mask body will not drip onto the part. Also, the mask body functions as a jig for supporting the part to be painted.
A part painting apparatus according to the invention may be constructed such that a paint drip guide for leading excess paint that may drip from the mask body to a predetermined position that does not interfere with spray painting is formed on the mask body, extending along the side opposite the surface to be painted of the part.
Even if excess paint that drips from the mask body does not drip onto the part to be painted, if it drips between the paint gun and the surface to be painted it may adhere to the surface to be painted due to the pressure of the spray painting. Otherwise, if excess paint drips directly onto the paint gun, the paint gun may become fouled such that proper spray is inhibited. Therefore, a paint drip guide is extended to a predetermined position so that excess paint does not drip between the paint gun and the surface to be painted or directly onto the paint gun.
Further, the mask body may be provided with a slant adjusting means for adjusting the slant angle with respect to vertical. Using a slant adjusting means, a configuration may be obtained whereby excess paint that drips from the mask body does not drip onto the part or the paint nozzle due to appropriate adjustment of the slant of the mask body with respect to vertical.
A plurality of mask bodies may be provided on a turntable corresponding to a first position where an operator attaches/detaches a part, and a second position where a paint gun performs spray painting. In addition, each of the mask bodies may be rotatably mounted with respect to the turntable. The rear surfaces of the mask bodies in the first and second positions face the outside of the turntable.
When the turntable is rotated, one of the mask bodies on the turntable is placed in a first position where the operator attaches/detaches a part, and the other mask body then in a second position where the paint gun performs spray painting. In the first position, a part which has been painted is removed from the mask body and a new part is attached to the mask body. During this time, the paint gun spray paints the surface to be painted of the part in the second position.
The mask body may be formed in a frame shape in which the inside is open and the surface to be painted of the part is exposed facing downward inside the frame. In this case, the frame (mask body) surrounding the surface to be painted inhibits the spray paint from leaking outside the mask body.
The part to be painted may be a lens which is a part of a lamp fixture for vehicular use. In this case, if dripping paint were to adhere to the lens, drops of paint could be seen through the lens, detracting from the appearance of the lens, or adhered drops of paint could alter the light distribution pattern of the lamp. Because, according to the invention, drops of paint do not adhere to the lens, these types of problems do not occur.